Chiral cyclodextrins

Figure 3.8 Second-dimension chiral cyclodextrin capillary column separation of a non-racemic pair of nonachlorobomane compounds extracted from dolphin blubber, shown with expanded attenuation in the inset. The primary separation (not shown) was performed on an apolar primary capillary column. Reproduced from H.-J. de Geus et al. J. High Resol. Chromatogr. 1998, 21, 39 (59).

In accordance with Emery s retro-hydroxamate ferrichrome, mentioned above, two retro analogs of the linear ferrioxamine G and cyclic desferrioxamine E (129 and 130, respectively) were prepared. The iron-chelating properties were compared to DFO, showing that the linear retro-desferrioxamine G (131) binds iron faster and the cyclic retro desferrioxamine E (132) has improved affinity to iron, compared to the linear DFO. Based on these resnlts, many retro-hydroxamate ferrioxamines were prepared. In a later paper, Akiyama and coworkers reported the attachment of -cyclodextrin, a cyclic oligosaccharide, composed of seven a-D-glucopyranoside units, linked from position 1 to position 4, to linear retro-hydroxamate ferrioxamines (133 and 134), which formed 1 1 iron(III) complexes. Influenced by the chiral -cyclodextrin gronp, 133 and 134 formed A-selective coordination around the metal ion. In addition, Akiyama proposed that the... 

In a search for more effective approaches to the problem of stereoselective dioxygenation, alternative methods have been developed. While the inclusion of alkenes and O2 within a chiral cyclodextrin cavity furnished hydroperoxides with modest ee values, neighboring stereocenters and chiral auxiliaries could induce highly stereoselective dioxygenation. In 1987 Kropf and Reichwaldt, and three years later Adam and coworkers reported on the photooxygenation of phenyl-substituted alkenes 36 producing allyUc hydroperoxides 37 and 38 with high diastereoselectivity (dr 80/20). In the best example... 

The extracts contained almost pure pheromone, with only minor amounts of other components. By comparison with synthetic samples, derivatization, and gas chromatography on a chiral cyclodextrin phase, the pheromone was identified as a 95 5 mixture of (5)- and (/ )-enantiomers of dimethyl citrate (cupilure (3), Fig. 4.2). Only the (5)-enantiomer was active (Tichy et al., 2001). Cupilure is probably present in ionized form on the silk (pK 3.5), because solvent extracts were neutral. The ionized carboxyl group may be conjugated to basic amino acids of the silk proteins. This would also explain why the pheromone is not volatile, despite its relatively low molecular weight, and is easily washed from the silk by water, including rain. In the tropical habitat of C. salei this would ensure the presence of cupilure only on freshly laid silk. 

Supelco. 1998. Chiral Cyclodextrin Capillary GC Columns. Sigma-Aldrich, Bellefonte, Penn. 

CDs bonded to polymer-based gel) Keystone ft-OH and Keystone / -PM YMC Chiral cyclodextrin BR,... 

Schiirch, S., Saxer, A., Claude, S., Tabacchi, R., Trusch, B., and Hulliger, J. (2001) Semi-preparative gas chromatographic separation of ah-trans-perhydrotriphenylene enantiomers on a chiral cyclodextrin stationary phase, J. Chromatogr. A 905, 175-182. 

The above phases represent the most common phases used in solving nearly all of the frequently encountered application problems. There are many other stationary phases which are produced to tune the phase polarity for specific applications. In addition to these phases, there are liquid crystalline, chiral, cyclodextrin, polymers such as polystyrene, divinylben-zene, molecular sieves, and alumina, which are designed for specific separation problems. The chemistry of fused silica deactivation and stationary-phase application, bonding, and cross-linking has been reviewed in detail [3,4]. 

Chiral cyclodextrins, crown ethers, and macrocyclic antibiotics in chiral separations using capillary electrophoresis 00CRV3715. 

Phosphorus-containing chiral cyclodextrins, calixarenes, and cyclophanes 06COC2307. 

Mertzman M.D., Foley J.P., Chiral cyclodextrin modified microemulsion electrokinetic chromatography. Electrophoresis, 25, 1188—1200 (2004). 

A Selection Guide to DEXTM Columns Stable derivatized cyclodextrin stationary phases for high resolution analyses of optical and positional isomers. In Chiral Cyclodextrin Capillary GC Columns. Sigma-Aldrich Co. Available at http // vww.sigmaaldrich.eom/etc/medialib/docs/Supelco/Bulletin/6504.Par.0001.File.tmp/ 6504.pdf. 

Cyclodextrins (and their derivatives) have been used widely in analytical chemistry, in particular, in separation technology. They have been incorporated into chromatographic applications, such as thin layer chromatography, gas chromatography, capillary electrophoresis and high performance liquid chromatography (HPLC), for the separation of similar chemical substances and even enantiomers (cyclodextrins are chiral). Conventional chiral HPLC columns are costly. A normal column containing an immobilised chiral cyclodextrin, such that one enantiomer forms a more stable complex over the other, can drastically reduce the cost. 

Mertzman, M. and Foley, J. 2004, Chiral cyclodextrin-modifled microemulsion electrokinetic chromatography. Electrophoresis 25, 1188. 

Authenticity assessment of genuine substances of coriander oil (Coriander sativum L.) has been the object of a work dealing with the analysis of 10 authentic coriander essential oil samples of different origins [29]. The techniques used were GC-IRMS and enantioselective two-dimensional GC using a chiral cyclodextrin derivative as the stationary phase. The enantiomer ratio and the 8 C values of 12 characteristic components were compared with those of commercially available... 

Chiral (cyclodextrin) Polar Adsorption H-bonding dipolar interactions steric effects... 

Buffer additives Urea, surfactants, complexing agents, organic solvents Buffer additives Urea, surfactants, inorganic salts, organic solvents, sulfonic acids, chiral cyclodextrins, amines... 

Grafting a receptor moiety onto rare earth metal complexes led to a new series of CSRs operating in water. Dy + complexes with cyclodextrin derivatives 75 (scheme 16) were synthesized as Itybrid-type CSRs in which the triaminotetracarboxylic acid moiety chelates the rare earth ion while the chiral cyclodextrin accommodates aromatic compounds in its hydrophobic pocket (Wenzel et al., 1994, 2000). Wenzel et al. (2003) demonstrated that the commercially available sulfonated and carboxymethylated cyclodextrins are effective CSRs for water-soluble aromatic cations in the presence of Dy + or Yb " ". A crown ether derivative, which accommodates primary ammonium cations, also forms chelates with rare earth... 

---